1. Field of the Invention
The present invention relates to a process for forming in a ferroelectric a microstructure to be favorably used for an optical parts or the like.
2. Related Art Statement
In order to form a microstructure such as an optical waveguide layer on a surface of a ferroelectric single crystal substrate, a given protecting mask is formed on the surface of the substrate, and a portion of the substrate exposed outside through an opening of the mask is selectively etched (For example, see The Transaction of the Institute of Electronics, Information and Communication Engineers) C-1 Vol. J77-C-I No. 5 (1994) pp 229-237).
In this case, the dimensional precision, the configuration precision, the height, etc. of the microstructure depend mainly upon a difference in etching rate (selective ratio) between the material of the protecting mask and that of the substrate for an etching agent. For this reason, the selective ratio needs to be generally 1: not less than 1, preferably 1: not less than 10 so that the microstructure having practical dimensional precision and configuration precision.
However, it was difficult to work substrates made of ferroelectric single crystals such as lithium niobate single crystal and lithium tantalate single crystal, because there is unavailable an appropriate protective masking material giving such a high selective ratio for them. Therefore, it has been practically difficult to form a microstructure, such as a ridged optical waveguide layer or a micro recess, having a practical configuration precision and a practical dimensional precision on the surface of the ferroelectric single crystal.